It is hard to know when the key and lock were invented. They might be the most ancient security mechanism. The lock can be used in almost any places where precious articles need to be protected in any forms, for example, a lock for jewelry box or a door lock. Please refer to FIG. 1. A conventional set of key and lock is shown. A key 1 and a lock 2 are paired for use. The lock 2 has a locking mechanism 3. When the lock 2 works (locks), the locking mechanism 3 is firmly keeping a loop so that and rigid item enclosed can be restricted and its free movement is limited. This helps increase security of the enclosed item because it can not be moved at will. When the item needs to be used, the key 3 is plugged into a key hole 4. With a torque applied to the key 3 to unlock, the locking mechanism 3 is released.
Locks have numerous types of locks, such as warded locks, pin tumbler lock, wafer tumbler locks, etc. Sizes of the locks vary. No matter what the form of lock is or how large it is, for the key owner, the structure of key must satisfy below requirements: convenient carrying, difficult duplication, low cost (comparing with the corresponding lock) and easy use. Sometimes, people need more keys for a shared lock; for instance, members of a family use the same key for the front door lock. It incurs another issue, management of key distribution. How can people use the same key without a risk of misuse by any irrelevant person? Another solution, user identification, comes along.
There are lots of user identifications can be used. For example, companies usually use passwords for a second safeguard. Passwords are difficult for people to memorize, especially when they need to keep numbers of passwords for different usages. A commonly used form of key becomes E-cards which contain necessary information of the user and the password to replace people's memory. However, any people having ordinary skills in the art will know how to duplicate the E-cards. Security encounters challenges. It pushes inventers to look for more securable way to make safer keys. Biometrics is a very good choice.
Biometrics refers to the identification of humans by their characteristics or traits, for example, fingerprint, face recognition, DNA, Palm print, hand geometry, iris recognition, retina, tec. Biometrics is used in computer science as a form of identification and access control. Therefore, a combination of advantages of conventional keys and biometrics becomes a trend for security.
Among all the biometrics, fingerprint is most used feature for identification. It is not only people have been studying fingerprint for centuries, but there are already many electronic readers (modules) can be used for design. U.S. Pat. No. 6,671,808 has disclosed a USB compliant personal key which is a good example of application of fingerprint. The invention makes the USB key safer in use with the help of personal identification. However, it is pity that the '808 is a pure electronic key. There are no physical key patterns or mechanism which helps protection of data copy.
On the other hand, a trend of electronic devices is to make products as compact as possible. Therefore, when a compound key uses any electronic components, its dimension can not be large for carrying.
In summary, a compound key having below features is still desired: convenient carrying, difficult duplication, low cost, easy use, and compact size of biometric module for identification.